Immunological assays for antibodies to the causative organism of syphilis (Treponema pallidum) in the blood of patients heretofore have been carried out by the Treponema pallidum Hemagglutination test (TPHA), the Fluorescent Treponema Antibody Absorption test (FTA-Abs) and the Trepenoma pallidum Immobilization test (TPI). These assays require a subjective estimate of antibody titer. An accurate assay in which the results are objectively determined is desirable since the results are more reproducible and can be realistically compared between different laboratories. In addition, it is desirable to have an assay in which the procedure as well as the final readout are amenable to automation.